Fig. 2.

Increasing rates of NH₄⁺ consumption by the whole culture after the addition of ammonium to an enrichment culture performing nitrite-dependent anaerobic methane oxidation. (A) On day 50, ammonium was added to the medium. Consumption was measured on day 55. The ammonium concentrations in the medium could be increased to 20 mM at day 160 (about 400 ml day⁻¹). (B) To determine the proportions of nitrite consumption by anammox and n-damo bacteria, the conversion rates of the coculture were measured on day 142. When nitrite and ammonium were both present (day 0 to 2.8 h), the total nitrite consumption was 15.4 nmol min⁻¹ mg protein⁻¹ (open diamonds) and the ammonium consumption was 9.0 nmol min⁻¹ mg protein⁻¹ (closed circles). When ammonium was depleted, nitrite was consumed at 5.0 nmol min⁻¹ mg protein⁻¹ (closed triangles).